[Thu-P1-027] Pheromone-induced odour learning and outstanding detection abilities in the newborn rabbit

International audience

English. Perception of the wide, complex and changing odour environment requires that the olfactory system engages processing mechanisms ensuring efficient detection and discrimination of stimuli ending in specific motor actions and in adaptation. In newborn rabbits detecting and responding to the mammary pheromone (MP) emitted by the mother is crucial for survival, since the MP is a strong releaser of typical head-searching/oral grasping behaviour allowing to locate and orally grasp the maternal nipples during the daily nursing. Strikingly, the MP also functions as a natural reinforcer, i.e. as an unconditioned stimulus able to promote appetitive conditioning to a new odorant (CS) in a single and very brief (5 min) association. We have already shown that such MP-induced odour learning, which involves peripheral plasticity (induction) and cerebral plasticity, results in an increase in detection threshold of the CS. These results were obtained when the CS was used at a single concentration (10-5 g/ml). Here, we investigated whether and how the use of a CS (ethyl isobutyrate) at different concentrations (from 10-5 to 10-23 g/ml) during pairing with the MP, influences post-conditioning detection threshold of the CS. The results highlight that the lower the CS concentration, the lower the detection threshold. However, below a certain concentration level, the response range no longer includes the highest CS concentrations but shifts and focuses around the conditioning concentration. These results are original both because they pinpoint 1) detection capability of a learned odorant at exceptionally low concentrations, and 2) that for low concentrations, the perceived quality of the CS is altered. The study provides a novel insight into olfactory perceptual sensitivity in neonates, as well as evidence of discontinuity in perceived odorant quality at very low intensity.